`Masonry` means any porous inorganic substrate, such as building materials. Gypsum is calcium sulfate dihydrate having the formula CaSO.sub.4 2H.sub.2 O. Masonry materials containing gypsum include gypsum wallboard and gypsum fiberboard. When calcium sulfate dihydrate is heated above 110.degree. C., moisture is evolved and the resulting product is termed plaster of paris or stucco. When plaster of paris is mixed with water, it rehydrates and sets to a solid mass within a few minutes. Gypsum wallboard can be produced by layering slabs of the solid mass between sheets of fabric or tough paper.
Alternatively, gypsum wallboard can be produced continuously by pouring a mixture comprising gypsum and water onto a conveyer belt and allowing the mixture to set before cutting boards to length and drying. Gypsum blocks, moldings, and the like can be prepared by forming a mixture comprising gypsum and water in a mold or casting to provide products with desired shapes. Drying times vary depending on the bulk of the mixture to be dried.
Masonry materials containing gypsum may further comprise organic, mineral or glass fibers to modify the physical properties of the materials. Suitable organic fibers include cellulosic fibers and paper.
Gypsum wallboard and other masonry materials containing gypsum have little resistance to water. Water repellence is an important factor in masonry construction. Moisture absorption in masonry can cause or contribute to problems such as expansion, shrinkage, cracking, staining, mildew, lowered resistance to freezing and thawing, chemical attack, corrosion of reinforcing steel, and damage to structures from settling. Therefore, it is an object of this invention to provide a water repellent composition for masonry materials containing gypsum.
Attempts have been made in the past to improve the water resistance of gypsum containing masonry materials by coating the materials with water repellent surface coatings and by incorporation of water resistant materials into the mixtures used to prepare the materials. Such water resistant materials include metallic soaps, asphalts, waxes, and resins. However, waterproofing by surface coating the masonry materials is insufficient because water resistance is provided only at the surface and the bulk of the substrate is left untreated. Therefore, it is a further object of this invention to provide a water repellent composition that can be uniformly dispersed in a gypsum containing masonry material.
Water repellent compositions that can be dispersed in a masonry material are exemplified by the following: U.S. Pat. No. 4,975,122 discloses a slurry of water, gypsum, and a composition comprising an admixture of an organic amine and an SiH containing siloxane.
U.S. Pat. No. 5,110,684 discloses a method of rendering masonry architectural building materials water repellent by incorporating an additive into the materials. The additive comprises a mixture of a water soluble silane coupling agent and an aqueous emulsion of a siloxane fluid. The silane coupling agent is an aminofunctional silane.
U.S. Pat. No. 5,855,667 discloses a gypsum mixture containing a hydrophobic additive. The mixture is prepared by adding gypsum and two alkoxysilanes to water. Thereafter, the gypsum mixture is formed into desired shapes and dried.
However, no polyvinyl alcohols are disclosed in U.S. Pat. Nos. 4,975,122, 5,110,684, 5,855,667, or 5,776,245. U.S. Pat. No. 5,776,245 discloses a method for hydrophobing gypsum. The method comprises preparing an aqueous gypsum mixture having a hydrophobic additive dispersed therein. The hydrophobic additive contains non-emulsified ingredients including an alkoxysilane and a polysiloxane. This patent teaches that the use of emulsified ingredients diminishes the hydrophobic properties in the gypsum mixture.
However, all of the gypsum containing materials described above suffer from the drawback that water repellence is still insufficient for some applications. Therefore, it is an object of this invention to produce a composition for rendering gypsum containing masonry materials water repellent. It is a further object of this invention to provide water repellent gypsum containing materials having superior water repellency to materials known in the art.
By using an organohydrogensiloxane emulsion, better distribution of the organohydrogensiloxane in the gypsum matrix can be obtained. Without wishing to be bound by theory, the applicants believe that the mechanism for increased water repellency is hydrogen bonding of the organohydrogensiloxane and the water within the gypsum matrix. The aminofunctional compounds catalyze the organohydrogensiloxane emulsion polymer into a siloxane resin.